1. Field of the Invention
The present invention relates to a pellicle for photolithography using a light having a wavelength of from 100 to 200 nm.
2. Discussion of Background
A pellicle is a dustproof integral device to be mounted on a photomask or a reticle (hereinafter referred to as a mask) so as to prevent dust particles from depositing on the mask and to prevent pattern failure during exposure, used in photolithography as one step in production of semiconductor devices or liquid crystal display boards. Usually, it has a structure such that a transparent thin membrane bonded to a frame by an adhesive is mounted on the mask at some distance from the mask surface.
In fields of production of semiconductor devices and liquid crystal display panels in which such a pellicle is used, the wavelength of light sources to be used has been shortened rapidly also in photolithography, along with minimization of wiring and wiring interval. In a conventional exposure technique with a minimum pattern dimension of at least 0.3 μm, a process employing an i-beam light source (365 nm) has been mainly used, and as a material of a transparent thin membrane of a pellicle (hereinafter referred to as a pellicle membrane), a cellulose nitrate type material has been used.
In recent years, for a photolithographic patterning process with a minimum pattern dimension of less than 0.3 μm, a KrF excimer laser is being introduced, but its irradiation wavelength is 248 nm, and the cellulose nitrate type membrane material is inadequate in durability. Further, it has been found that an amorphous perfluoropolymer is effective as a membrane material in a case where a light having a short wavelength such as an excimer laser is employed (Japanese Patent No. 2951337 or Japanese patent No. 2952962).
On the other hand, for a photolithographic patterning process with a minimum pattern dimension of at most 0.2 μm under development in recent years, it has been proposed to use, as a laser having a short wavelength of from 100 to 200 nm, e.g. an argon fluoride excimer laser having a wavelength of 193 nm (hereinafter referred to as an ArF excimer laser) or a fluorine gas excimer laser having a wavelength of 157 nm (hereinafter referred to as a F2 excimer laser).
However, these laser lights have an extremely high energy, whereby even the above amorphous perfluoropolymer as disclosed in Japanese Patent No. 2951337 is inadequate in durability. For example, “CYTOP” (tradename) which is a perfluoropolymer used in the above patent, has had a problem that the durability against such laser lights is not practically adequate although it has high transparency at 193 nm. Further, its light transmittance and durability suddenly decrease at a wavelength shorter than 170 nm, and its transmittance of the F2 excimer laser light having a wavelength of 157 nm is very low.
Therefore, as a pellicle membrane which is durable against the F2 excimer laser light, a fluoropolymer as disclosed in JP-A-2001-330943 or a polymer containing a perfluoro-1,3-dioxol as disclosed in W0200137044, has, for example, been proposed for a pellicle membrane or for an adhesive to bond the pellicle membrane to the frame.
However, with such a fluoropolymer, the durability is still not fully satisfactory although it has high transparency at 157 nm. Also the adhesive to fix the pellicle membrane to the frame has had a similar problem of degradation due to reflected light or scattering light of the laser. Thus, it has been desired to develop an adhesive having high durability.